The present invention is generally directed to fuel cells and more specifically to balance of plant components of high temperature fuel cell systems and their operation.
Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. High temperature fuel cells include solid oxide and molten carbonate fuel cells. These fuel cells may operate using hydrogen and/or hydrocarbon fuels. There are classes of fuel cells, such as the solid oxide regenerative fuel cells, that also allow reversed operation, such that oxidized fuel can be reduced back to unoxidized fuel using electrical energy as an input.
While diesel is a readily available fuel, it contains long chain hydrocarbons (Paraffins, Olefins, Napthenes and Aromatics) which are difficult to reform. Issues with reformation can lead to formation of coke within the reforming reactor. These formations can cause a failure of any system using diesel reformation. Use of diesel fuel within most types of fuel cell systems requires some sort of reformation process to convert the diesel to a hydrogen rich reformate or syngas (CO+H2 mixture). Because of the problems with reformation, construction of a prior art fuel cell system powered by diesel fuel has been difficult.
Proposed solutions in the prior art use the concept of pre-reformation in which the diesel fuel is pre-conditioned, breaking larger hydrocarbons into smaller ones. The pre-reformation step is conducted in a catalyst containing pre-reformer via a catalyst mediated reformation reaction. Then, a subsequent standard reforming step is performed on the smaller hydrocarbons. This solution presents issues of thermal integration and can result in a loss of overall system efficiency. Furthermore, because a pre-reforming catalyst must be provided, the cost of the total system is increased.